The invention relates to a belt pulley for a belt drive and a plastic injection molding method for producing the belt pulley. The belt pulley comprises an anti-friction bearing and a plastic running ring that surrounds the anti-friction bearing and with which the outer ring of the anti-friction bearing is injection molded. One end side of the running ring has a plurality of molding points that run on the sector radii of circular sectors that have a common center point on the rotational axis of the belt pulley and at least two center point angles of different sizes.
Such belt pulleys are typically used in belt drives of internal combustion engines for tensioning or switching the belt. To keep the operating noises of the belt drive to the lowest possible level, it is known from DE 103 60 290 B4 to keep the vibrational excitation of the belt resulting from the out-of-roundness of the running ring small. This is possible through the special shaping for the plastic injection molding of the running ring and in reality through the positioning of the injection molding points that are distributed in non-uniform angular positions on the end side of the running ring. In this way, the out-of-roundness that is unavoidable in injection molding can be defined for the running ring and distributed sufficiently non-uniformly over the belt running surface. Through this detailed shaping, above all, the especially undesired resonance effects in the belt drive can be prevented.
The non-uniform angular distribution of the injection molding points, however, causes a filling progress that is non-uniform in time for the injection molding cavity with plastic melt, wherein the process-dependent increase in pressure produces non-round deformation of the anti-friction bearing outer ring at the end of the injection molding process and this deformation leads to the development of operating noises and premature failure of the anti-friction bearing.